LECTURE 1 Dr Ali El-Agamey CHEM-323: Polynuclear Aromatic Hydrocarbon CHEM-323: Polynuclear Aromatic Hydrocarbon DAMIETTA UNIVERSITY 1

LECTURE 1

Dr Ali El-Agamey

CHEM-323:

Polynuclear Aromatic Hydrocarbon

CHEM-323:


DAMIETTA UNIVERSITY

1

Understand the principles of biphenyl nomenclature and the different methods used in its synthesis.

Understand the various methods involved in the synthesis of the different isolated polynuclear aromatic compounds.

Appreciate the effect of phenyl group on the stability of various intermediates.

Appreciate the steric effect of phenyl and benzyl groups.

Understand the role of phenyl and benzyl groups in electrophilic substitution reactions.

LEARNING OUTCOMES

LECTURES 1-2

LEARNING OUTCOMES

LECTURES 1-2

2

Lecture 1-2: -Nomeclature, synthesis and reactions of biphenyl.

-Synthesis and reactions of diphenylmethane, triphenylmethane, triphenylmethyl chloride, triphenylmethanol, trans-stilbene and benzoin.

-Nomenclature of fused systems.

Lecture 3-6: -Aromatic character of fused systems.

-Structure elucidation of naphthalene

-Reactions of naphthalene.

Lecture 7-11: - Synthesis of naphthalene.

- Synthesis and reactions of anthracene and phenanthrene.

Lecture 12: -General revision for the whole course.

Reading

RT Morrison and RN Boyd, Organic Chemistry, Allyn and Bacon, Inc., 1987.

Mundy, BP et al, Name reactions and reagents in organic synthesis, Wiley, 2005

H Meislich et al, Organic Chemistry, McGraw-Hill Book Company, 1980.

IL Finar, Organic Chemistry, Volume 1 (1985) and Volume 2 (1977).

Reading

RT Morrison and RN Boyd, Organic Chemistry, Allyn and Bacon, Inc., 1987.

Mundy, BP et al, Name reactions and reagents in organic synthesis, Wiley, 2005

H Meislich et al, Organic Chemistry, McGraw-Hill Book Company, 1980.

IL Finar, Organic Chemistry, Volume 1 (1985) and Volume 2 (1977). 3

Isolated ringsIsolated rings

(1) Biphenyl(1) Biphenyl

NomenclatureNomenclature

4

Polynuclear Aromatic HydrocarbonsPolynuclear Aromatic Hydrocarbons

Homework: Give name for the following compounds

Homework: Give name for the following compounds

Br Br

(H3C)2N N(CH3)2

Cl

ClCO2H

(a)(b)

(c)

5


SynthesisSynthesis

(a) Fittig’s reaction

(c) Gomberg reaction

(b) Gattermann reaction

More examples 6

2 PhBr + 2 Na + 2 NaBrPh–Ph

+ 2 N22 PhN2+Cl– Cu

HeatPh–Ph

+ N2NaOH+ Ar–H + NaCl + H2OArN2

+Cl– Ar–Ar

(d) Ullmann coupling reaction

(e) Benzidine rearrangement

7

+ CuI22 Ar–ICuHeat

Ar–Ar

More examples

Ph–NH–NH–Ph

Hydrazobenzene

PhNO2

Zn/NaOH

H+

Benzidine

NH2H2N

(i) NaNO2/HCl

(ii) H3PO2

Biphenyl


ReactionsReactions

Although –NO2 is m-directing group, p-O2NC6H4 is p-directing!!

According to the charge distribution approach, a p-nitro group would have been expected to direct to the m-position in the other ring.

N

O

O

N

O

O

N

O

O8


ReactionsReactions

However, the stabilities of the carbocation intermediates generatedfollowing o- and p-substitutions are greater than that generated from m-substitution due to the greater dispersal of charge in the formersubstitutions. Therefore, o-and p-substitutions are preferred.

O2N NO2O2N NO2

p–substitution

O2N

NO2

O2N

NO2

m–substitution9

(2) Diphenylmethane(2) Diphenylmethane

Synthesis and reactionsSynthesis and reactions

10

(3) Triphenylmethane (Tritane)(3) Triphenylmethane (Tritane)


Homework: write the product of the following reaction

Homework: write the product of the following reaction

11

H+

NN

CH3

CH3

LECTURE 2

Dr Ali El-Agamey

CHEM-323:


CHEM-323:


DAMIETTA UNIVERSITY

12

(3) Triphenylmethyl chloride (Trityl chloride)

(3) Triphenylmethyl chloride (Trityl chloride)

Ag2 Ph3CCl

C6H6, no air2 Ph3C Dimer

(White solid)Yellow colour

Ph3C–CPh3

was believed to be

Hexaphenylethane

Actually

H

Ph3C

Real dimer product

13

(4) Triphenylmethanol

(Triphenylcarbinol)

(4) Triphenylmethanol

(Triphenylcarbinol)


14

(5) trans-Stilbene

(trans-1,2-Diphenylethene)

(5) trans-Stilbene

(trans-1,2-Diphenylethene)


(6) Benzoin(6) Benzoin


Homework: Complete the following equation

15

Homework: Write the mechanism of the following reaction

CHO

OMe

KCN ???

S

(1) KOH

O

O(2) HCl

S

HO CO2H

16

Naphthalene, anthracene and phenanthrene are obtained from coal tar, naphthalene being the most abundant (5%) of all constituents of coal tar.

Uses: moth balls, which contain naphthalene, are used as insect repellants (naphthalene is very volatile).

Many synthetic dyes contain naphthalene moiety.

Naphthalene

Fused rings

17

How many isomers for monosubstitution of naphthalene (C8H7X)?

Nomenclature of naphthalene, anthracene and phenanthrene

Fused rings

How many isomers for monosubstitution of anthracene (C14H9X)?

How many isomers for monosubstitution of phenanthrene (C14H9X)?

18

How many isomers for disubstitution of naphthalene (C8H6X2)?

How many isomers for disubstitution of naphthalene (C8H6XY)?

Homework

How many isomers for disubstitution of anthracene (C14H8X2)?

How many isomers for disubstitution of phenanthrene (C14H8X2)?

In each case write the name of each isomer?

19

Nomenclature of naphthalene, anthracene and phenanthrene

CH3

(a)

Br

(b)

ClI

(c)

(a) (b) (c)

NO2

O2N

SO3H

H2N

OH

NO2

NO2

SO3H

NO2

(a) (b) (c)

20

Homework: Give names for the following compounds

(d)

CO2HCl

(a)

NO2

NO2(b)

(c)

LECTURE 3

Dr Ali El-Agamey

CHEM-323:


CHEM-323:


DAMIETTA UNIVERSITY

21

22

Undergo electrophilic substitution reactions.

Like benzene, they are unusually stable as indicated from their low heats of hydrogenation and combustion.

Aromatic character of naphthalene, anthracene and phenanthrene

Naphthalene, anthracene and phenanthrene are classified as aromatic because of their properties, which resemble those of benzene.

(i) Experimental point of view

23

Resonance Energy

24

Resonance energy of A = 61 kcal mol-1

Resonance energy of B = 84 kcal mol-1

Resonance energy of C = 92 kcal mol-1

Resonance energy of benzene = 36 kcal mol-1


(A) (B) (C)

25

Flat (sp2-hybidized); cyclic

-cloud above and below the plane due to ???

HÜckel`s rule ???


(ii) Theoretical point of view: they have the structure required for aromatic compounds

26

Resonance structures and bond lengths of naphthalene, anthracene and phenanthrene

There are n+1 principal resonance structures for polynuclear aromatic hydrocarbon containing n benzene rings fused together in a linear manner.

Bond length

Double bond character

The different carbon-carbon bond lengths reveal the decreased aromaticity of fused polynuclear aromatic hydrocarbons.

Phenanthrene is an angular polynuclear aromatic hydrocarbon.

Fused ringsFused rings

27

Naphthalene, anthracene and phenanthrene are obtained from coal tar.

Naphthalene being the most abundent (5%) of all constituentsof coal tar.

(a) Uses

In moth balls as insect repellants.

Many synthetic dyes contain naphthalene moiety.

(1) Naphthalene(C10H8)

(b) Structure Elucidation

Reactivity of naphthalene as compared to benzeneReactivity of naphthalene as compared to benzene

28

In naphthalene, two fused rings share a pair of –electrons, therefore the aromaticity and the resonance energy per ring is less than that of benzene itself.

Resonance energy of naphthalene = 61 kcal mol-1

Resonance energy per ring = 30.5 kcal mol-1

Resonance energy of benzene = 36 kcal mol-1

Stability of the compound increases

Stability of the compound increasesAs R.E. increasesAs R.E. increases

Resistance to destroy aromatic

character increases

Resistance to destroy aromatic

character increases

Reactivity

decreases

Reactivity

decreases

Reactivity of naphthalene as compared to benzeneReactivity of naphthalene as compared to benzene

29

What happened when aromatic character of one ring of naphthalene is destroyed?

Therefore, naphthalene undergoes oxidation or reduction more readily than benzene but only to the stage where a substituted benzene is formed; further oxidation or reduction requires more vigorous conditions.

30

(1) Oxidation

Reactions of naphthaleneReactions of naphthalene

O

CO2H

CO2H

O

O

O

O

O2, V2O5 CrO3

AcOH

HNO3

1,4-Naphthoquinone

O

O

CH3CH3 CrO3

AcOH

31

(1) Oxidation


Oxidation by V2O5 is important industrial process (naphthalene is available from coal tar).

Vitamins K1 and K2 are derivatives of 1,4-naphthoquinone.

Because of this tendency to form quinones, it is not always feasible to prepare naphthalenecarboxylic acids by oxidation of methyl side chains.

32

(2) Reduction


Na, C5H11OH H2, Pt or Ni

Na, C2H5OH

H2, Pt or Ni

Tetralin Decalin

1,4-Dihydronaphthalene

33

(3) Electrophilic susbstitution reactions


1-Substitution versus 2-substitution

Number of resonance structures Aromatic sextet is retained (benzene has large R. E.)

Fries rule: The most stable arrangement of a polynuclear compound is that form which has the maximum number of rings in the benzenoid condition.

Carbocation and T.S. resulting from attack at the 1-position are much more stable than those resulting from attack at the 2-position . Therefore, 1-susbstitution will be preferred.

34

(i) Nitration


NO2

HNO3, H2SO4 Red.

NH2

NaNO2, HCl

N2 Cl

LECTURE 4

Dr Ali El-Agamey

CHEM-323:


CHEM-323:


DAMIETTA UNIVERSITY

35

Reactions of naphthalene: Nitration; Halogenation; Chloromethylation; Friedel-Crafts reactions (alkylation and acylation).

Sulfonation.

Naphthols and naphthylamines.

Synthesis of 1-substituted naphthalenes.

Synthesis of 2-substituted naphthalenes.

Summary of naphthalene reactions.

LEARNING OUTCOMES

LECTURE 4

LEARNING OUTCOMES

LECTURE 4

36

37

(i) Nitration


NO2

HNO3, H2SO4 Red.

NH2

NaNO2, HCl

N2 Cl

38

(ii) Halogenation


Br

Br2, CCl4,

No Lewis acid needed

Mg

MgBr

X

X2, FeX = Cl, Br

Introduction of NO2 and X groups opens the way to the preparation of a series of 1-substituted naphthalenes.

39

(iii) Chloromethylation


Friedel-Crafts reactions is carried out under mild conditions.

CH2O, HCl

CH2Cl

(iv) Friedel-Crafts reactions

Friedel-Crafts alkylation is of little use because (1) polyalkylation and (2) side reactions.

Alkylnaphthalenes can be prepared via acylation or ring closure.

40


NaOCl,

CH3COCl

AlCl3

COCH3

COCH3

Solvent: CS2 or

C2H2Cl4

Solvent: C6H5NO2NaOCl,

CO2H

CO2H

(iv) Friedel-Crafts reactions

Acetylation affords access to the preparation of a series of 2-substituted naphthalenes.

41


(v) Sulfonation

SO3H

SO3H

Conc H2SO4, 80 oC

Conc H2SO4, 160 oC

Conc H2SO4, 160 oC

42


(v) Sulfonation

43

At low T, 1-S is formed faster than 2-S

E2 > E1

However, at high T, which speeds up a reaction, or if the reaction is left for long time, 2-S becomes the main product.

Therefore, 1-S is called kinetically controlled product

k1 > k2

Δ H2 > Δ H1 E-2 (E2 + Δ H2) >> E-1 (E1 + Δ H1) k-1 >> k-2

1-S reforms N much faster than does 2-S and hence 2-S accumulates at the expense of 1-S i.e. the equilibrium is established in favor of the formation of 2-S, which is called the thermodynamically controlled product.

44

The lower stability of 1-S is attributed to the steric interaction between the sulfonic group and the hydrogen atom in the 8-position.

(v) Sulfonation

45


SO3H

SO3H

PCl5

PCl5

Cl

Cl

46


Naphthols and naphthylamines

SO3Na NaOH,Fusion

ONa dil H2SO4OH

NH2

dil H2SO4

OH

+ NH3

OH NH3, (NH4)2SO3

, PressureNH2

Bucherer reaction

47


Naphthols and naphthylamines

OH

FeCl3OHHO

Violet-blue ppt

-Binaphthol

OHFeCl3

OH

OH

Green ppt

-Binaphthol

48

Synthesis of 1-substituted naphthalenesSynthesis of 1-substituted naphthalenes

NO2 NH2 N2 Cl

X MgX

Synthesis of 2-substituted naphthalenesSynthesis of 2-substituted naphthalenes

SO3H OH NH2

N2 ClXMgX

Acetylation and sulfonation affords access to the preparation of a series of 2-substituted naphthalenes.

NH2NO2

50

Summary of naphthalene reactionsSummary of naphthalene reactions

Documents

LECTURE 1 Dr Ali El-Agamey CHEM-323: Polynuclear Aromatic Hydrocarbon CHEM-323: Polynuclear Aromatic Hydrocarbon DAMIETTA UNIVERSITY 1